1. Field of the Invention:
This invention relates generally to a process for the preparation of 2,3-dimethoxy-5-methylbenzoquinone and, more specifically, to a one-stage process for the production of 2,3-dimethoxy-5-methylbenzoquinone by oxidation of 3,4,5trimethoxytoluene with hydrogen peroxide using, as a catalyst, a heteropolyacid containing molybdenum or tungsten and phosphorus or silicon as two heteronucleus metal elements thereof.
2. Description of the Prior Art
2,3-Dimethoxy-5-methylbenzoquinone is an important intermediate compound for a quinone-type antitumor agent or a coenzyme Q. One known method of preparing 2,3-dimethoxy-5-methylbenzoquinone includes coupling 3,4,5-trimethoxytoluene with a p-nitrobenzenediazonium salt to form an azo compound, reducing the azo compound to form an o-toluidine derivative, and oxidizing the o-toluidine derivative (Japanese Examined Patent Publication No. 38-11,981). This process is, however, low in efficiency because of its multi-step process and requires a large amount of an oxidizing agent, leading to the production of a large amount of industrial waste as a by-product.
One well known one stage process for the production of 2,3-dimethoxy-5-methylbenzoquinone includes oxidizing 3,4,5-trimethoxytoluene using a hexacyanoferrate as a catalyst (J. Org. Chem., 50, 1766 (1985)). This process has a problem that the catalyst contains highly toxic cyano ions. Furthermore, the yield of the benzoquinone with this process is not satisfactory.